Kenichi Koyanagi

Infrared absorption peak due to Ta=O bonds in Ta2O5 thin films

Ta2O5 films deposited on Si substrates were investigated using transmission Fourier-transform infrared spectroscopy. We found a new absorption peak at 2340 cm−1 that can be characterized as a stretching vibration mode due to Ta=O bonds in the films. This peak appeared following annealing in O2 ambient, but not in N2 ambient. It was located at 2335 cm−1 in amorphous Ta2O5 films and shifted to 2340 cm−1 after crystallization by annealing at over 700 °C. The bonds associated with the peak were homogeneously distributed in the film. We demonstrated that Ta2O5 films can include strong double bonds between Ta and O (Ta=O) in the structure, independent of whether they are crystalline or amorphous.

Formation of silicon–oxide layers at the interface between tantalum oxide and silicon substrate

Silicon–oxide layers formed at the tantalum–oxide/silicon interface were investigated by using Fourier transform infrared spectroscopy (FTIR). The samples were annealed in oxygen atmosphere, in nitrogen atmosphere, and in vacuum. It has been found that the formation of the interfacial silicon–oxide layers depends neither on the tantalum–oxide thickness nor on the annealing atmosphere, but on the annealing temperature. The silicon–oxide layer is formed even by annealing in vacuum. It is concluded that the silicon–oxide layer is formed not by a diffusion of the oxygen from the annealing atmosphere, but by a reaction between the tantalum–oxide film and the Si substrate. FTIR analysis and transmission electron microscopy of the interfacial layer show that the silicon–oxide layer has a bonding configuration different from a pure silicon dioxide.

Formation mechanism of interfacial Si–oxide layers during postannealing of Ta2O5/Si

The Si–O–Si bonds formed at the Ta2O5/Si interface by annealing were investigated by using Fourier transform infrared absorption spectroscopy. The Ta2O5 thin films deposited on Si substrates were annealed in different ambient (H2O, O2, and N2) at temperatures between 500 and 800 °C. When annealing is done in H2O, the interfacial silicon–oxide grows very rapidly, because the oxidation species can easily diffuse through Ta2O5 films, and because the Si–O formation is controlled by the diffusion of H2O in the interfacial layer. When annealing is done in O2, the oxidation species can also easily diffuse through Ta2O5, but not through the interfacial layer. The interfacial layer is formed by a reaction between Ta2O5 and Si even if the annealing ambient does not contain oxidation species, as is the case when annealing is done in N2. We conclude that the Si–O formation during postannealing in O2 and N2 is controlled by the diffusion of the Si from the substrate through the interfacial layer with an activation ene...

Ta-O phonon peaks in tantalum oxide films on Si

Abstract Ta 2 O 5 films, 10 and 100 nm in thickness, directly deposited on a Si substrate were investigated by using transmission Fourier-transform infrared spectroscopy. The samples were annealed in dry oxygen, wet oxygen and nitrogen atmospheres. The Ta–O phonon peaks in the infrared absorption spectra appeared at 210, 510 and 570 cm −1 in samples that were annealed at 700 and 800°C for up to 4 h. We found that the 510/570 cm −1 peak height ratio is larger for thicker Ta 2 O 5 films annealed at higher temperatures. This implies that peak height ratios are directly related to Ta 2 O 5 film quality, and we conclude that stronger lattice structures can be formed by annealing at higher temperatures.

Stability and Application to Multilevel Metallization of Fluorine-Doped Silicon Oxide by High-Density Plasma Chemical Vapor Deposition

We report the application of biased high-density-plasma-chemical-vapor-deposited (HDP-CVD) SiOF films to multilevel metallization technology. We discuss the reason for the SiOF films low dielectric constant and illustrate the optimal deposition conditions. The fluorine concentration in the HDP-CVD SiOF film can affect the gap filling characteristics. We observed that the dielectric constant of this SiOF film is 3.7 for a fluorine concentration of 7.3 at.%. This film was successfully applied to intermetal dielectrics and the parasitic capacitance was 13% lower than that of a SiO2 film.

Integration Issues for Low Dielectric Constant Materials in each Generation of ULSI'S

The technologies utilizing Fluorinated Silicon Oxide (FSG, k=3.6) and Hydrogen Silsesquioxane (HSQ, k=3.0) have been established for 0.25-µm and 0.1 8-µm generation ULSIs. However, low-k materials for the next generation ULSIs, which have a dielectric constant of less than 3.0, have not become mature yet. In this paper, we review process integration issues in applying FSG and HSQ, and describe integration results and device performance using Fluorinated Amorphous Carbon (a-C:F, k=2.5) as one of the promising low-k materials for the next generation ULSIs.